Golf ball having multi-layer cover with unique outer cover characteristics

ABSTRACT

The present invention is directed to an improved multi-layer golf ball comprising a core, an inner cover layer and an outer cover layer. The inner cover layer is comprised of a low acid ionomer blend which may or may not include a filler such as zinc-stearate. The outer cover layer is comprised of a soft, non-ionomeric thermoplastic or thermosetting elastomer such as polyurethane, polyester or polyesteramide. The resulting multi-layered golf ball of the present invention provides for enhanced distance without sacrificing playability or durability when compared to known multi-layer golf balls.

CROSS REFERENCES TO RELATED APPLICATIONS

This application is a continuation application of U.S. application Ser.No. 09/776,278 filed Feb. 2, 2001, which is a continuation applicationof U.S. application Ser. No. 09/470,196 filed on Dec. 21, 1999, now U.S.Pat. No. 6,210,293, which is a continuation application of U.S.application Ser. No. 08/870,585 filed Jun. 6, 1997 now abandoned, whichis a continuation of U.S. application Ser. No. 08/556,237 filed Nov. 9,1995, now abandoned, which is a continuation-in-part of U.S. applicationSer. No. 08/070,510 filed on Jun. 1, 1993, now abandoned.

FIELD OF THE INVENTION

The present invention relates to golf balls and, more particularly, toimproved standard and oversized golf balls comprising multi-layer coverswhich have a comparatively hard inner layer and a relatively soft outerlayer such as that produced by the use of a polyurethane based outerlayer. The improved multi-layer golf balls provide for enhanced distanceand durability properties over single layer cover golf balls while atthe same time offering enhanced “feel” and spin characteristicsgenerally associated with soft balata and balata-like covers of theprior art.

BACKGROUND OF THE INVENTION

Traditional golf ball covers have been comprised of balata or blends ofbalata with elastomeric or plastic materials. The traditional balatacovers are relatively soft and flexible. Upon impact, the soft balatacovers compress against the surface of the club producing high spin.Consequently, the soft and flexible balata covers provide an experiencedgolfer with the ability to apply a spin to control the ball in flight inorder to produce a draw or a fade, or a backspin which causes the ballto “bite” or stop abruptly on contact with the green. Moreover, the softbalata covers produce a soft “feel” to the low handicap player. Suchplayability properties (workability, feel, etc.) are particularlyimportant in short iron play with low swing speeds and are exploitedsignificantly by relatively skilled players.

Despite all the benefits of balata, balata covered golf balls are easilycut and/or damaged if mis-hit. Golf balls produced with balata orbalata-containing cover compositions therefore have a relatively shortlifespan.

As a result of this negative property, balata and its syntheticsubstitutes, transpolyisoprene and transpolybutadiene, have beenessentially replaced as the cover materials of choice by new covermaterials comprising ionomeric resins.

Ionomeric resins are polymers containing interchain ionic bonding. Asresult of their toughness, durability and flight characteristics,various ionomeric resins sold by E. I. DuPont de Nemours & Company underthe trademark Surlyn® and more recently, by the Exxon Corporation (seeU.S. Pat. No. 4,911,451) under the trademarks—“Escor®” and the tradename “lotek®”, have become the materials of choice for the constructionof golf ball covers over the traditional “balata” (transpolyisoprene,natural or synthetic) rubbers. As stated, the softer balata covers,although exhibiting enhanced playability properties, lack the durability(cut and abrasion resistance, fatigue endurance, etc.) propertiesrequired for repetitive play.

Ionomeric resins are generally ionic copolymers of an olefin, such asethylene, and a metal salt of an unsaturated carboxylic acid, such asacrylic acid, methacrylic acid, or maleic acid. Metal ions, such assodium or zinc, are used to neutralize some portion of the acidic groupin the copolymer resulting in a thermoplastic elastomer exhibitingenhanced properties, i.e. durability, etc., for golf ball coverconstruction over balata. However, some of the advantages gained inincreased durability have been offset to some degree by the decreasesproduced in playability. This is because although the ionomeric resinsare very durable, they tend to be very hard when utilized for golf ballcover construction, and thus lack the degree of softness required toimpart the spin necessary to control the ball in flight. Since theionomeric resins are harder than balata, the ionomeric resin covers donot compress as much against the face of the club upon impact, therebyproducing less spin. In addition, the harder and more durable ionomericresins lack the “feel” characteristic associated with the softer balatarelated covers.

As a result, there are currently more than fifty (50) commercial gradesof ionomers available both from DuPont and Exxon, with a wide range ofproperties which vary according to the type and amount of metal cations,molecular weight, composition of the base resin (i.e., relative contentof ethylene and methacrylic and/or acrylic acid groups) and additiveingredients such as reinforcement agents, etc. However, a great deal ofresearch continues in order to develop a golf ball cover compositionexhibiting not only the improved impact resistance and carrying distanceproperties produced by the “hard” ionomeric resins, but also theplayability (i.e., “spin”, “feel”, etc.) characteristics previouslyassociated with the “soft” balata covers, properties which are stilldesired by the more skilled golfer.

Consequently, a number of two-piece (a solid resilient center or corewith a molded cover) and three-piece (a liquid or solid center,elastomeric winding about the center, and a molded cover) golf ballshave been produced by the present inventor and others to address theseneeds. The different types of materials utilized to formulate the cores,covers, etc. of these balls dramatically alter the balls' overallcharacteristics.

In addition, multi-layered covers containing one or more ionomer resinshave also been formulated in an attempt to produce a golf ball havingthe overall distance, playability and durability characteristicsdesired. For example, this was addressed by Spalding & EvenfloCompanies, Inc., the assignee of the present invention, in U.S. Pat. No.4,431,193 where a multi-layered, regular sized, golf ball is disclosed.

In the '193 patent, a multi-layer golf ball is produced by initiallymolding a first cover layer on a spherical core and then adding a secondlayer. The first layer is comprised of a hard, high flexural modulusresinous material such as type 1605 Surlyn® (now designated Surlyn®8940). Type 1605 Surlyn® (Surlyn® 8940) is a sodium ion based low acid(less than or equal to 15 weight percent methacrylic acid) ionomer resinhaving a flexural modulus of about 51,000 psi. An outer layer of acomparatively soft, low flexural modulus resinous material such as type1855 Surlyn® (now designated Surlyn® 9020) is molded over the innercover layer. Type 1855 Surlyn® (Surlyn® 9020) is a zinc ion based lowacid (10 weight percent methacrylic acid) ionomer resin having aflexural modulus of about 14,000 psi.

The '193 patent teaches that the hard, high flexural modulus resin whichcomprises the first layer provides for a gain in coefficient ofrestitution over the coefficient of restitution of the core. Theincrease in the coefficient of restitution provides a ball which servesto attain or approach the maximum initial velocity limit of 255 feet persecond as provided by the United States Golf Association (U.S.G.A.)rules. The relatively soft, low flexural modulus outer layer providesessentially no gain in the coefficient of restitution but provides forthe advantageous “feel” and playing characteristics of a balata coveredgolf ball.

Unfortunately, however, while a ball of the '193 patent does exhibitenhanced playability characteristics with improved distance (i.e.enhanced C.O.R. values) over a number of other then known multi-layeredballs, the ball suffers from poor cut resistance and relatively shortdistance (i.e. lower C.O.R. values) when compared to two-piece, singlecover layer balls commercially available today. These undesirableproperties make the ball produced in accordance with the '193 patentunacceptable by today's standards.

The present invention is directed to new multi-layer golf ballcompositions which provide for enhanced coefficient of restitution (i.e,enhanced resilience or carrying distance) and/or durability propertieswhen compared to the multi-layer balls found in the prior art, as wellas improved outer cover layer softness and durability. As such, theplayability characteristics (i.e., “feel”, “click”, “spin”, etc.) arenot diminished.

These and other objects and features of the invention will be apparentfrom the following summary and description of the invention, thedrawings and from the claims.

SUMMARY OF THE INVENTION

The present invention is directed to improved multi-layer golf ballcover compositions and the resulting multi-layer golf balls producedusing the improved compositions. The novel multi-layer golf ball coversof the present invention include a first or inner layer or ply of a highacid (greater than 16 weight percent acid) ionomer blend or, morepreferably, a low acid (16 weight percent acid or less) ionomer blendand second or outer layer or ply comprised of a comparatively softer,low modulus ionomer, ionomer blend or other non-ionomeric thermoplasticor thermosetting elastomer such as polyurethane or polyester elastomer.The multi-layer golf balls of the invention can be of standard orenlarged size. Preferably, the inner layer or ply includes a blend oflow acid ionomers and has a Shore D hardness of 60 or greater and theouter cover layer comprised of polyurethane and has a Shore D hardnessof about 45 (i.e., Shore C hardness of about 65).

It has been found that multi-layer golf balls having inner and outercover layers exhibit higher C.O.R. values and have greater traveldistance in comparison with balls made from a single cover layer. Inaddition, it has been found that use of an inner cover layer constructedof a blend of low acid (i.e., 16 weight percent acid or less) ionomerresins produces softer compression and higher spin rates than innercover layers constructed of high acid ionomer resins. This is compoundedby the fact that the softer polyurethane outer layer adds to thedesirable “feel” and high spin rate while maintaining respectableresiliency. The soft outer layer allows the cover to deform more duringimpact and increases the area of contact between the club face and thecover, thereby imparting more spin on the ball. As a result, the softpolyurethane cover provides the ball with a balata-like feel andplayability characteristics with improved distance and durability.

Consequently, the overall combination of the inner and outer coverlayers made from blends of low acid ionomer resins and polyurethaneresults in a standard size or oversized golf ball having enhancedresilience (improved travel distance) and durability (i.e. cutresistance, etc.) characteristics while maintaining and in manyinstances, improving the balls playability properties.

The combination of a low acid ionomer blend inner cover layer with asoft, relatively low modulus ionomer, polyurethane based elastomer outercover layer provides for good overall coefficient of restitution (i.e.,enhanced resilience) while at the same time demonstrating improvedcompression and spin. The outer cover layer generally contributes to amore desirable feel and spin, particularly at lower swing speeds withhighly lofted clubs such as half wedge shots.

Two principal properties involved in golf ball performance areresilience and hardness. Resilience is determined by the coefficient ofrestitution (C.O.R.), the constant “e” which is the ratio of therelative velocity of two elastic spheres after direct impact to thatbefore impact. As a result, the coefficient of restitution (“e”) canvary from 0 to 1, with 1 being equivalent to an elastic collision and 0being equivalent to an inelastic collision.

Resilience (C.O.R.), along with additional factors such as club headspeed, angle of trajectory and ball configuration (i.e., dimple pattern)generally determine the distance a ball will travel when hit. Since clubhead speed and the angle of trajectory are factors not easilycontrollable by a manufacturer, factors of concern among manufacturersare the coefficient of restitution (C.O.R.) and the surfaceconfiguration of the ball.

The coefficient of restitution (C.O.R.) in solid core balls is afunction of the composition of the molded core and of the cover. Inballs containing a wound core (i.e., balls comprising a liquid or solidcenter, elastic windings, and a cover), the coefficient of restitutionis a function of not only the composition of the center and cover, butalso the composition and tension of the elastomeric windings. Althoughboth the core and the cover contribute to the coefficient ofrestitution, the present invention is directed to the enhancedcoefficient of restitution (and thus travel distance) which is affectedby the cover composition.

In this regard, the coefficient of restitution of a golf ball isgenerally measured by propelling a ball at a given speed against a hardsurface and measuring the ball's incoming and outgoing velocityelectronically. As mentioned above, the coefficient of restitution isthe ratio of the outgoing velocity to the incoming velocity. Thecoefficient of restitution must be carefully controlled in allcommercial golf balls in order for the ball to be within thespecifications regulated by the United States Golf Association(U.S.G.A.). Along this line, the U.S.G.A. standards indicate that a“regulation” ball cannot have an initial velocity (i.e., the speed offthe club) exceeding 255 feet per second. Since the coefficient ofrestitution of a ball is related to the ball's initial velocity, it ishighly desirable to produce a ball having sufficiently high coefficientof restitution to closely approach the U.S.G.A. limit on initialvelocity, while having an ample degree of softness (i.e., hardness) toproduce enhanced playability (i.e., spin, etc.).

The hardness of the ball is the second principal property involved inthe performance of a golf ball. The hardness of the ball can affect theplayability of the ball on striking and the sound or “click” produced.Hardness is determined by the deformation (i.e., compression) of theball under various load conditions applied across the ball's diameter(i.e., the lower the compression value, the harder the material). Asindicated in U.S. Pat. No. 4,674,751, softer covers permit theaccomplished golfer to impart proper spin. This is because the softercovers deform on impact significantly more than balls having “harder”ionomeric resin covers. As a result, the better player is allowed toimpart fade, draw or backspin to the ball thereby enhancing playability.Such properties may be determined by various spin rate tests such as the“nine iron” spin rate test described below in the Examples.

Accordingly, the present invention is directed to an improvedmulti-layer cover which produces, upon molding each layer around a core(preferably a solid core) to formulate a multi-layer cover, a golf ballexhibiting enhanced distance (i.e., resilience) without adverselyaffecting, and in many instances, improving the ball's playability(hardness/softness) and/or durability (i.e., cut resistance, fatigueresistance, etc.) characteristics.

These and other objects and features of the invention will be apparentfrom the following detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a golf ball embodying the inventionillustrating a core 10 and a cover 12 consisting of an inner layer 14and an outer layer 16 having dimples 18; and

FIG. 2 is a diametrical cross-sectional view of a golf ball of theinvention having a core 10 and a cover 12 made of an inner layer 14 andan outer layer 16 having dimple 18.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to improved multi-layer golf balls,particularly a golf ball comprising a multi-layered cover 12 over asolid core 10, and method for making same.

The multi-layered cover 12 comprises two layers: a first or inner layeror ply 14 and a second or outer layer or ply 16. The inner layer 14 iscomprised of a low acid (i.e. 16 weight percent acid or less) ionomerblend. Preferably, the inner layer is comprised of a blend of two ormore low acid (i.e. 16 weight percent acid or less) ionomer resinsneutralized to various extents by different metal cations. The innercover layer may or may not include a metal stearate (e.g., zincstearate) or other metal fatty acid salt. The purpose of the metalstearate or other metal fatty acid salt is to lower the cost ofproduction without affecting the overall performance of the finishedgolf ball.

The low acid ionomers which may be suitable for use in formulating theinner layer compositions of the subject invention are ionic copolymerswhich are the metal, i.e., sodium, zinc, magnesium, etc., salts of thereaction product of an olefin having from about 2 to 8 carbon atoms andan unsaturated monocarboxylic acid having from about 3 to 8 carbonatoms. Preferably, the ionomeric resins are copolymers of ethylene andeither acrylic or methacrylic acid. In some circumstances, an additionalcomonomer such as an acrylate ester (i.e., iso- or n-butylacrylate,etc.) can also be included to produce a softer terpolymer. Thecarboxylic acid groups of the copolymer are partially neutralized (i.e.,approximately 10-75%, preferably 30-70%) by the metal ions. Each of thelow acid ionomer resins which may be included in the inner layer covercompositions of the invention contains 16% by weight or less of acarboxylic acid.

The inner layer compositions include the low acid ionomers such as thosedeveloped and sold by E. I. DuPont de Nemours & Company under thetrademark Surlyn® and by Exxon Corporation under the trademarks Escor®or tradename lotek®, or blends thereof.

The low acid ionomeric resins available from Exxon under the designationEscor® and or lotek®, are somewhat similar to the low acid ionomericresins available under the Surlyn® trademark. However, since theEscor®/lotek® ionomeric resins are sodium or zinc salts ofpoly(ethylene-acrylic acid) and the Surlyn® resins are zinc, sodium,magnesium, etc. salts of poly(ethylene-methacrylic acid), distinctdifferences in properties exist.

When utilized in the construction of the inner layer of a multi-layeredgolf ball, it has been found that the low acid ionomer blends extend therange of compression and spin rates beyond that previously obtainable.More preferably, it has been found that when two or more low acidionomers, particularly blends of sodium and zinc high acid ionomers, areprocessed to produce the covers of multi-layered golf balls, (i.e., theinner cover layer herein) the resulting golf balls will travel furtherand at an enhanced spin rate than previously known multi-layered golfballs. Such an improvement is particularly noticeable in enlarged oroversized golf balls.

For example, the normal size, multi-layer golf ball taught in U.S. Pat.No. 4,650,193 does not incorporate blends of low acid ionomeric resinsof the present invention in the inner cover layer. In addition, themulti-layered ball disclosed in the '193 patent suffers substantially indurability in comparison with the present invention.

Furthermore, as shown in the Examples, use of an inner layer formulatedfrom blends of lower acid ionomers produces multi-layer golf ballshaving enhanced compression and spin rates. These are the propertiesdesired by the more skilled golfer.

With respect to the outer layer 16 of the multi-layered cover of thepresent invention, the outer cover layer is comparatively softer thanthe low acid ionomer blend based inner layer. The softness provides forthe enhanced feel and playability characteristics typically associatedwith balata or balata-blend balls. The outer layer or ply, is comprisedof a relatively soft, low modulus (about 1,000 psi to about 10,000 psi)and low acid (less than 16 weight percent acid) ionomer, ionomer blendor a non-ionomeric elastomer such as, but not limited to, apolyurethane, a polyester elastomer such as that marketed by DuPontunder the trademark Hytrel®, a polyurethane sold by BASF under thedesignation Baytec®or a polyether amide such as that marketed by ElfAtochem S. A. under the trademark Pebax®. The outer layer is fairly thin(i.e. from about 0.010 to about 0.070 in thickness, more desirably 0.03to 0.06 inches in thickness for a 1.680 inch ball and 0.04 to 0.07inches in thickness for a 1.72 inch ball), but thick enough to achievedesired playability characteristics while minimizing expense.

Preferably, the outer layer includes a blend of hard and soft (low acid)ionomer resins such as those described in U.S. Pat. Nos. 4,884,814 and5,120,791, both incorporated herein by reference. Specifically, adesirable material for use in molding the outer layer comprises a blendof a high modulus (hard), low acid, ionomer with a low modulus (soft)low acid, ionomer to form a base ionomer mixture. A high modulus ionomerherein is one which measures from about 15,000 to about 70,000 psi asmeasured in accordance with ASTM method D-790. The hardness may bedefined as at least 50 on the Shore D scale as measured in accordancewith ASTM method D-2240.

A low modulus ionomer suitable for use in the outer layer blend has aflexural modulus measuring from about 1,000 to about 10,000 psi, with ahardness of about 20 to about 40 on the Shore D scale.

The hard ionomer resins utilized to produce the outer cover layercomposition hard/soft blends include ionic copolymers which are thesodium, zinc, magnesium or lithium salts of the reaction product of anolefin having from 2 to 8 carbon atoms and an unsaturated monocarboxylicacid having from 3 to 8 carbon atoms. The carboxylic acid groups of thecopolymer may be totally or partially (i.e. approximately 15-75 percent)neutralized.

The hard ionomeric resins are likely copolymers of ethylene and eitheracrylic and/or methacrylic acid, with copolymers of ethylene and acrylicacid being the most preferred. Two or more types of hard ionomericresins may be blended into the outer cover layer compositions in orderto produce the desired properties of the resulting golf balls.

As discussed earlier herein, the hard ionomeric resins introduced underthe designation Escor® and sold under the designation lotek® aresomewhat similar to the hard ionomeric resins sold under the Surlyn®trademark. However, since the lotek® ionomeric resins are sodium or zincsalts of poly(ethylene-acrylic acid) and the Surlyn® resins are zinc orsodium salts of poly(ethylene-methacrylic acid) some distinctdifferences in properties exist. As more specifically indicated in thedata set forth below, the hard lotek® resins (i.e., the acrylic acidbased hard ionomer resins) are the more preferred hard resins for use informulating the outer layer blends for use in the present invention. Inaddition, various blends of lotek® and Surlyn® hard ionomeric resins, aswell as other available ionomeric resins, may be utilized in the presentinvention in a similar manner.

Examples of commercially available hard ionomeric resins which may beused in the present invention in formulating the inner and outer coverblends include the hard sodium ionic copolymer sold under the trademarkSurlyn® 8940 and the hard zinc ionic copolymer sold under the trademarkSurlyn® 9910. Surlyn® 8940 is a copolymer of ethylene with methacrylicacid and about 15 weight percent acid which is about 29 percentneutralized with sodium ions. This resin has an average melt flow indexof about 2.8. Surlyn® 9910 is a copolymer of ethylene and methacrylicacid with about 15 weight percent acid which is about 58 percentneutralized with zinc ions. The average melt flow index of Surlyn® 9910is about 0.7. The typical properties of Surlyn® 9910 and 8940 are setforth below in Table 1:

TABLE 1 Typical Properties of Commercially Available Hard Surlyn ®Resins Suitable for Use in the Inner and Outer Layer Blends of thePresent Invention ASTM D 8940 9910 8920 8528 9970 9730 Cation TypeSodium Zinc Sodium Sodium Zinc Zinc Melt flow index, D-1238 2.8 0.7 0.91.3 14.0 1.6 gm/10 min. Specific Gravity, D-792 0.95 0.97 0.95 0.94 0.950.95 g/cm³ Hardness, Shore D D-2240 66 64 66 60 62 63 Tensile Strength,D-638 (4.8) (3.6) (5.4) (4.2) (3.2) (4.1) (kpsi), MPa 33.1 24.8 37.229.0 22.0 28.0 Elongation, % D-638 470 290 350 450 460 460 FlexuralModulus, D-790 (51) (48) (55) (32) (28) (30) (kpsi) MPa 350 330 380 220190 210 Tensile Impact (23° C.) D-1822S 1020 1020 865 1160 760 1240KJ/m₂(ft.-lbs./in²) (485) (485) (410) (550) (360) (590) Vicat SofteningD-1525 63 62 58 73 61 73 Temperature, ° C.

Examples of the more pertinent acrylic acid based hard ionomer resinssuitable for use in the present inner and outer cover composition soldunder the lotek® trademark by the Exxon Corporation include lotek® 4000,lotek® 4010, lotek® 8000, lotek® 8020 and lotek® 8030. The typicalproperties of these and other lotek® hard ionomers suited for use informulating the inner and outer layer cover composition are set forthbelow in Table 2:

TABLE 2 Typical Properties of Iotek ® Ionomers Resin ASTM PropertiesMethod Units 4000 4010 8000 8020 8030 Cation type zinc zinc sodiumsodium sodium Melt index D-1238 g/10 min. 2.5 1.5 0.8 1.6 2.8 DensityD-1505 kg/m³ 963 963 954 960 960 Melting Point D-3417 ° C. 90 90 90 87.587.5 Crystallization Point D-3417 ° C. 62 64 56 53 55 Vicat SofteningPoint D-1525 ° C. 62 63 61 64 67 % Weight Acrylic Acid 16 11 % of AcidGroups cation neutralized 30 40 Plaque ASTM Properties Method Units 40004010 8000 8020 8030 (3 mm thick, compression molded) Tensile at breakD-638 MPa 24 26 36 31.5 28 Yield point D-638 MPa none none 21 21 23Elongation at break D-638 % 395 420 350 410 395 1% Secant modulus D-638MPa 160 160 300 350 390 Shore Hardness D D-2240 — 55 55 61 58 59 FilmProperties (50 micron film 2.2:1 Blow-up ratio) 4000 4010 8000 8020 8030Tensile at Break MD D-882 MPa 41 39 42 52 47.4 TD D-882 MPa 37 38 38 3840.5 Yield point MD D-882 MPa 15 17 17 23 21.6 TD D-882 MPa 14 15 15 2120.7 Elongation at Break MD D-882 % 310 270 260 295 305 TD D-882 % 360340 280 340 345 1% Secant modulus MD D-882 MPa 210 215 390 380 380 TDD-882 MPa 200 225 380 350 345 Dart Drop Impact D-1709 g/micron 12.4 12.520.3 Resin ASTM Properties Method Units 7010 7020 7030 Cation type zinczinc zinc Melt Index D-1238 g/10 min. 0.8 1.5 2.5 Density D-1505 kg/m³960 960 960 Melting Point D-3417 ° C. 90 90 90 Crystallization PointD-3417 ° C. — — — Vicat Softening D-1525 ° C. 60 63 62.5 Point % WeightAcrylic Add % of Acid Groups Cation Neutralized Plaque ASTM PropertiesMethod Units 7010 7020 7030 (3 mm thick, compression molded) Tensile atbreak D-638 MPa 38 38 38 Yield Point D-638 MPa none none none Elongationat break D-638 % 500 420 395 1% Secant modulus D-638 MPa — — — ShoreHardness D D-2240 — 57 55 55

Comparatively, soft ionomers are used in formulating the hard/softblends of the inner and outer cover compositions. These ionomers includeacrylic acid based soft ionomers. They are generally characterized ascomprising sodium or zinc salts of a terpolymer of an olefin having fromabout 2 to 8 carbon atoms, acrylic acid, and an unsaturated monomer ofthe acrylate ester class having from 1 to 21 carbon atoms. The softionomer is preferably a zinc based ionomer made from an acrylic acidbase polymer in an unsaturated monomer of the acrylate ester class. Thesoft (low modulus) ionomers have a hardness from about 20 to about 40 asmeasured on the Shore D scale and a flexural modulus from about 1,000 toabout 10,000, as measured in accordance with ASTM method D-790.

Certain ethylene-acrylic acid based soft ionomer resins developed by theExxon Corporation under the designation lotek® 7520 (referred toexperimentally by differences in neutralization and melt indexes as LDX195, LDX 196, LDX 218 and LDX 219) may be combined with known hardionomers such as those indicated above to produce the inner and outercover layers. The combination produces higher C.O.R.s at equal or softerhardness, higher melt flow (which corresponds to improved, moreefficient molding, i.e., fewer rejects) as well as significant costsavings versus the inner and outer layers of multi-layer balls producedby other known hard-soft ionomer blends as a result of the lower overallraw materials costs and improved yields.

While the exact chemical composition of the resins to be sold by Exxonunder the designation lotek® 7520 is considered by Exxon to beconfidential and proprietary information, Exxon's experimental productdata sheet lists the following physical properties of the ethyleneacrylic acid zinc ionomer developed by Exxon:

TABLE 3 Physical Properties of Iotek ® 7520 Property ASTM Method UnitsTypical Value Melt Index D-1238 g/10 min. 2 Density D-1505 kg/m³ 0.962Cation Zinc Melting Point D-3417 ° C. 66 Crystallization Point D-3417 °C. 49 Vicat Softening Point D-1525 ° C. 42 Plaque Properties (2 mm thickCompression Molded Plaques) Tensile at Break D-638 MPa 10 Yield PointD-638 MPa None Elongation at Break D-638 % 760 1% Secant Modulus D-638MPa 22 Shore D Hardness D-2240 32 Flexural Modulus D-790 MPa 26 ZwickRebound ISO 4862 % 52 De Mattia Flex Resistance D-430 Cycles >5000Elongation at D412 % 490 Break Taber Abrasion D460, mg/1000 350 H-18cycles Part A Part B Component¹ , Properties (Isocyanate) (Resin)Viscosity @ 25° C., mPa · s 2500 2100 Density @ 25° C., g/cm 1.08 1.09NCO, % 9.80 — Hydroxyl Number, Mg KOH/g — 88 ¹Component A is a modifieddiphenylmethane diisocyanate (MDI) prepolymer and component B is apolyether polyol blend.

In addition, test data collected by the inventor indicates that lotek®7520 resins have Shore D hardnesses of about 32 to 36 (per ASTM D-2240),melt flow indexes of 3±0.5 g/10 min (at 190° C. per ASTM D-1288), and aflexural modulus of about 2500-3500 psi (per ASTM D-790). Furthermore,testing by an independent testing laboratory by pyrolysis massspectrometry indicates that lotek® 7520 resins are generally zinc saltsof a terpolymer of ethylene, acrylic acid, and methyl acrylate.

Furthermore, the inventor has found that a newly developed grade of anacrylic acid based soft ionomer available from the Exxon Corporationunder the designation lotek® 7510, is also effective, when combined withthe hard ionomers indicated above in producing golf ball coversexhibiting higher C.O.R. values at equal or softer hardness than thoseproduced by known hard-soft ionomer blends. In this regard, lotek® 7510has the advantages (i.e. improved flow, higher C.O.R. values at equalhardness, increased clarity, etc.) produced by the lotek® 7520 resinwhen compared to the methacrylic acid base soft ionomers known in theart (such as the Surlyn® 8625 and the Surlyn® 8629 combinationsdisclosed in U.S. Pat. No. 4,884,814).

In addition, lotek® 7510, when compared to lotek® 7520, producesslightly higher C.O.R. valves at equal softness/hardness due to thelotek® 7510's higher hardness and neutralization. Similarly, lotek® 7510produces better release properties (from the mold cavities) due to itsslightly higher stiffness and lower flow rate than lotek® 7520. This isimportant in production where the soft covered balls tend to have loweryields caused by sticking in the molds and subsequent punched pin marksfrom the knockouts.

According to Exxon, lotek® 7510 is of similar chemical composition aslotek® 7520 (i.e. a zinc salt of a terpolymer of ethylene, acrylic acid,and methyl acrylate) but is more highly neutralized. Based upon FTIRanalysis, lotek® 7520 is estimated to be about 30-40 wt.-% neutralizedand lotek® 7510 is estimated to be about 40-60 wt.-% neutralized. Thetypical properties of lotek® 7510 in comparison of those of lotek® 7520are set forth below:

TABLE 4 Physical Properties of Iotek ® 7510 in Comparison to Iotek ®7520 IOTEK ® 7520 IOTEK ® 7510 Ml, g/10 min 2.0 0.8 Density, g/cc 0.960.97 Melting Point, ° F. 151 149 Vicat Softening Point, ° F. 108 109Flex Modulus, psi 3800 5300 Tensile Strength, psi 1450 1750 Elongation,% 760 690 Hardness, Shore D 32 35

It has been determined that when hard/soft ionomer blends are used forthe outer cover layer, good results are achieved when the relativecombination is in a range of about 90 to about 10 percent hard ionomerand about 10 to about 90 percent soft ionomer. The results are improvedby adjusting the range to about 75 to 25 percent hard ionomer and 25 to75 percent soft ionomer. Even better results are noted at relativeranges of about 60 to 90 percent hard ionomer resin and about 40 to 60percent soft ionomer resin.

Specific formulations which may be used in the cover composition areincluded in the examples set forth in U.S. Pat. Nos. 5,120,791 and4,884,814. The present invention is in no way limited to those examples.

Moreover, in alternative embodiments, the outer cover layer formulationmay also comprise a soft, low modulus non-ionomeric thermoplasticelastomer including a polyester polyurethane such as B.F.GoodrichCompany's Estane® polyester polyurethane X-4517. According toB.F.Goodrich, Estane® X-4517 has the following properties:

Properties of Estane ® X-4517 Tensile 1430 100% 815 200% 1024 300% 1193Elongation 641 Youngs Modulus 1826 Hardness A/D 88/39 Dayshore Rebound59 Solubility in Water Insoluble Melt processing temperature >350° F.(>177° C.) Specific Gravity (H₂O = 1) 1.1-1.3

Other soft, relatively low modulus non-ionomeric thermoplasticelastomers may also be utilized to produce the outer cover layer as longas the non-ionomeric thermoplastic elastomers produce the playabilityand durability characteristics desired without adversely effecting theenhanced spin characteristics produced by the low acid ionomer resincompositions. Preferably, the non-ionomeric thermoplastic elastomershave a Shore D hardness of 64 or less. These include, but are notlimited to thermoplastic polyurethanes such as: Texin® thermoplasticpolyurethanes from Mobay Chemical Co. and the Pelletane® thermoplasticpolyurethanes from Dow Chemical Co.; Ionomer/rubber blends such as thosein Spalding U.S. Pat. Nos. 4,986,545; 5,098,105 and 5,187,013; and,Hytrel® polyester elastomers from DuPont and Pebax® polyesteramides fromElf Atochem S.A.

Similarly, a castable, thermosetting polyurethane produced by BASF underthe trade designation Baytec® has also shown enhanced cover formulationproperties. According to BASF, Baytec® (such as Baytec® RE 832), relatesto a group of reactive elastomers having outstanding wear resistance,high mechanical strength, high elasticity and good resistance toweathering, moisture and chemicals. The Baytec® RE-832 system gives thefollowing typical physical properties:

ASTM Test Property Method Unit Value Tear Strength D624 psi 180 Die CStress at 100% Modulus D412 psi 320 200% Modulus 460 300% Modulus 600Ultimate Strength D412 psi 900 Elongation at D412 % 490 Break TaberAbrasion D460, H-18 mg/1000 350 cycles Part A Part B Component¹Properties (Isocyanate) (Resin) Viscosity @ 25° C., mPa · s 2500 2100Density @ 25° C., g/cm 1.08 1.09 NCO, % 9.80 — Hydroxyl Number, Mg KOH/g— 88 ¹Component A is a modified diphenylmethane diisocyanate (MDI)prepolymer and component B is a polyether polyol blend.

In preparing golf balls in accordance with the present invention, a hardinner cover layer is molded (by injection molding or by compressionmolding) about a core (preferably a solid core). A comparatively softerouter layer is molded over the inner layer.

The conventional solid core is about 1.545 inches in diameter, althoughit can range from about 1.495 to about 1.575 inches. Conventional solidcores are typically compression molded from a slug of uncured or lightlycured elastomer composition comprising a high cis content polybutadieneand a metal salt of an α, β, ethylenically unsaturated carboxylic acidsuch as zinc mono or diacrylate or methacrylate. To achieve highercoefficients of restitution in the core, the manufacturer may includefillers such as small amounts of a metal oxide such as zinc oxide. Inaddition, larger amounts of metal oxide than those that are needed toachieve the desired coefficient are often included in conventional coresin order to increase the core weight so that the finished ball moreclosely approaches the U.S.G.A. upper weight limit of 1.620 ounces.Other materials may be used in the core composition including compatiblerubbers or ionomers, and low molecular weight fatty acids such asstearic acid. Free radical initiators such as peroxides are admixed withthe core composition so that on the application of heat and pressure, acomplex curing cross-linking reaction takes place.

The inner cover layer which is molded over the core is about 0.100inches to about 0.010 inches in thickness, preferably about 0.0375inches thick. The outer cover layer is about 0.010 inches to about 0.050inches in thickness, preferably 0.0300 inches thick. Together, the core,the inner cover layer and the outer cover layer combine to form a ballhaving a diameter of 1.680 inches or more, the minimum diameterpermitted by the rules of the United States Golf Association andweighing about 1.620 ounces.

Additional materials may be added to the cover compositions (both innerand outer cover layer) of the present invention including dyes (forexample, Ultramarine Blue sold by Whitaker, Clark and Daniels of SouthPlainsfield, N.J.) (see U.S. Pat. No. 4,679,795); pigments such astitanium dioxide, zinc oxide, barium sulfate and zinc sulfate; and UVabsorbers; antioxidants; antistatic agents; and stabilizers. Further,the cover compositions of the present invention may also containsoftening agents, such as plasticizers, processing aids, etc. andreinforcing material such as glass fibers and inorganic fillers, as longas the desired properties produced by the golf ball covers are notimpaired.

The various cover composition layers of the present invention may beproduced according to conventional melt blending procedures. In the caseof the outer cover layer, when a blend of hard and soft, low acidionomer resins are utilized, the hard ionomer resins are blended withthe soft ionomeric resins and with a masterbatch containing the desiredadditives in a Banbury mixer, two-roll mill, or extruder prior tomolding. The blended composition is then formed into slabs andmaintained in such a state until molding is desired. Alternatively, asimple dry blend of the pelletized or granulated resins and colormasterbatch may be prepared and fed directly into the injection moldingmachine where homogenization occurs in the mixing section of the barrelprior to injection into the mold. If necessary, further additives suchas an inorganic filler, etc., may be added and uniformly mixed beforeinitiation of the molding process. A similar process is utilized toformulate the low acid ionomer resin compositions used to produce theinner cover layer.

The golf balls of the present invention can be produced by moldingprocesses currently well known in the golf ball art. Specifically, thegolf balls can be produced by injection molding or compression moldingthe inner cover layer about wound or solid molded cores to produce anintermediate golf ball having a diameter of about 1.50 to 1.67 inches,preferably about 1.620 inches. The outer layer is subsequently moldedover the inner layer to produce a golf ball having a diameter of 1.680inches or more. Although either solid cores or wound cores can be usedin the present invention, as a result of their lower cost and superiorperformance, solid molded cores are preferred over wound cores.

In compression molding, the inner cover composition is formed viainjection at about 380° F. to about 450° F. into smooth surfacedhemispherical shells which are then positioned around the core in a moldhaving the desired inner cover thickness and subjected to compressionmolding at 200° to 30° F. for about 2 to 10 minutes, followed by coolingat 50° to 70° F. for about 2 to 7 minutes to fuse the shells together toform a unitary intermediate ball. In addition, the intermediate ballsmay be produced by injection molding wherein the inner cover layer isinjected directly around the core placed at the center of anintermediate ball mold for a period of time in a mold temperature offrom 50° F. to about 100° F. Subsequently, the outer cover layer ismolded about the core and the inner layer by similar compression orinjection molding techniques to form a dimpled golf ball of a diameterof 1.680 inches or more.

After molding, the golf balls produced may undergo various furtherprocessing steps such as buffing, painting and marking as disclosed inU.S. Pat. No. 4,911,451.

The resulting golf ball produced from the low acid ionomer resin innerlayer and the relatively softer, low flexural modulus outer layerprovide for an improved multi-layer golf ball which provides fordesirable coefficient of restitution, compression, spin and durabilityproperties while at the same time offering the feel characteristicsassociated with soft balata and balata-like covers of the prior art.

The present invention is further illustrated by the following examplesin which the parts of the specific ingredients are by weight. It is tobe understood that the present invention is not limited to the examples,and various changes and modifications may be made in the inventionwithout departing from the spirit and scope thereof.

EXAMPLE 1

Several intermediate balls (cores plus inner cover layers) were preparedin accordance with conventional molding procedures described above. Theinner cover compositions were molded around 1.545 inch diameter coresweighing 36.5 grams such that the inner cover had a wall thickness ofabout 0.0675 inches, with the overall ball measuring about 1.680 inchesin diameter.

The cores utilized in the examples were comprised of the followingingredients: high cis-polybutadiene, zinc diacrylate, zinc oxide, zincstearate, peroxide, calcium carbonate, etc. The molded cores exhibitedRiehle compressions of about 60 and C.O.R. values of about 0.800. Arepresentative formulation of the molded cores is set forth below:

MATERIAL WEIGHT BR-1220 (high cis-polybutadiene) 70.70 Taktene ® 220(high cis-polybutadiene) 29.30 React Rite ™ ZDA (zinc diacrylate) 31.14Zinc Oxide 6.23 Zinc Stearate 20.15 Limestone 17.58 Ground Flash 20.15(20-40 Mesh) Blue Masterbatch .012 Luperco ® 231XL .89 or Trigonox ®29/40 Papi ® 94 .50 ¹Blue Masterbatch consists of unknown compositionsused only for internal identification purposes and has no effect onphysical properties.

The inner cover compositions designated herein as compositions A-Eutilized to formulate the intermediate balls are set forth in Table 7below. The resulting molded intermediate balls were tested to determinethe individual compression (Riehle), C.O.R., Shore C hardness, spin rateand cut resistance properties. These results are also set forth in Table7 below.

The data of these examples are the average of twelve intermediate ballsproduced for each example. The properties were measured according to thefollowing parameters:

Coefficient of restitution (C.O.R.) was measured by firing the resultinggolf ball in an air cannon at a velocity of 125 feet per second againsta steel plate positioned 12 feet from the muzzle of the canon. Therebound velocity was then measured. The rebound velocity was divided bythe forward velocity to give a coefficient of restitution.

Shore hardness was measured generally in accordance with ASTM test 2240.

Cut resistance was measured in accordance with the following procedure:A golf ball is fired at 135 feet per second against the leading edge ofa pitching wedge wherein the leading edge radius is {fraction (1/32)}inch, the loft angle is 51 degrees, the sole radius is 2.5 inches andthe bounce angle is 7 degrees.

The cut resistance of the balls tested herein was evaluated on a scaleof 1 to 5. The number 1 represents a cut that extends completely throughthe cover to the core. A 2 represents a cut that does not extendcompletely through he cover but that does break the surface. A 3 doesnot break the surface of the cover but does leave a permanent dent. A 4leaves only a slight crease which is permanent but not as severe as 3. A5 represents virtually no visible indentation or damage of any sort.

The spin rate of the golf ball was measured by striking the resultinggolf balls with a pitching wedge or 9 iron wherein the club head speedis about 105 feet per second and the ball is launched at an angle of 26to 34 degrees with an initial velocity of about 110 to 115 feet persecond. The spin rate was measured by observing the rotation of the ballin flight using stop action Strobe photography.

Initial velocity is the velocity of a ball when struck at a hammer speedof 143.8 feet per second in accordance with a test as prescribed by theU.S.G.A.

As will be noted, compositions A, B and C include high acid ionomericresins (16% or more acid), with composition B further including zincstearate. Composition D represents the inner layer (i.e. Surlyn® 1605)used in U.S. Pat. No. 4,431,193. Composition E provides a hard, low acidionomeric resin blend.

The purpose behind producing and testing the balls of Table 5 was toprovide a subsequent comparison in properties with the multi-layer golfballs of the present invention.

TABLE 5 Molded Intermediate Golf Balls Ingredients of Inner CoverComposi- tions A B C D E Iotek ® 959 50 50 — — — Iotek ® 960 50 50 — — —Zinc — 50 — — — Stearate Surlyn ® — — 75 — — 8162 Surlyn ® — — 25 — —8422 Surlyn ® — — — 100 — 1605 Iotek ® — — — — 50 7030 Iotek ® — — — —50 8000 Properties of Molded Intermediate Balls Compression 58 58 60 6362 C.O.R. .811 .810 .807 .793 .801 Shore C 98 98 97 96 96 Hardness SpinRate 7,367 6,250 7,903 8,337 7,956 (R.P.M.) Cut 4-5 4-5 4-5 4-5 4-5Resistance

As shown in Table 5 above, the high acid ionomer resin inner cover layer(molded intermediate balls A-C) have lower spin rates and exhibit higherresiliency characteristics than the low acid ionomer resin based innercover layers of balls D and E.

Multi-layer balls in accordance with the present invention were thenprepared. Specifically, the inner cover compositions used to produceintermediate golf balls from Table 5 were molded over the solid cores toa thickness of about 0.0375 inches, thus forming the inner layer. Thediameter of the solid core with the inner layer measured about 1.620inches. Alternatively, the intermediate golf balls of Table 5 wereground down using a centerless grinding machine to a size of 1.620inches in diameter to produce an inner cover layer of 0.0375 inches.

The size of 1.620 inches was determined after attempting to mold theouter cover layer to various sizes (1.600″, 1.610″, 1.620″, 1.630″and1.640″) of intermediate (core plus inner layer) balls. It was determinedthat 1.620″was about the largest “intermediate” ball (i.e., core plusinner layer) which could be easily molded over with the soft outer layermaterials of choice. The goal herein was to use as thin an outer layeras necessary to achieve the desired playability characteristics whileminimizing the cost of the more expensive outer materials. However, witha larger diameter final golf ball and/or if the cover is compressionmolded, a thinner cover becomes feasible.

With the above in mind, an outer cover layer composition was blendedtogether in accordance with conventional blending techniques. The outerlayer composition used for this portion of the example is a relativelysoft cover composition such as those listed in U.S. Pat. No. 5,120,791.An example of such a soft cover composition is a 45% soft/55% hard lowacid ionomer blend designated by the inventor as “TE-90”. Thecomposition of TE-90 is set forth as follows:

Outer Cover Layer Composition TE-90 Iotek ® 8000 22.7 weight % Iotek ®7030 22.7 weight % Iotek ® 7520 45.0 weight % White MB¹  9.6 weight %¹White MB consists of about 23.77 weight percent TiO₂; 0.22 weightpercent Uvitex ® OB, 0.03 weight percent Santonox ® R, 0.05 weightpercent Ultramarine Blue ™ and 75.85 weight percent Iotek ® 7030.

The above outer layer composition was molded around each of the 1.620diameter intermediate balls comprising a core plus one of compositionsA-D, respectively. In addition, for comparison purposes, Surlyn® 1855(new Surlyn® 9020), the cover composition of the '193 patent, was moldedabout the inner layer of composition D (the intermediate ballrepresentative of the '193 patent). The outer layer TE-90 was molded toa thickness of approximately 0.030 inches to produce a golf ball ofapproximately 1.680 inches in diameter. The resulting balls (a dozenballs for each example) were tested and the various properties thereofare set forth in Table 6A as follows:

TABLE 6A Finished Balls Ingredients: 1 2 3 4 5 Inner A B C D D CoverComposi- tion Outer TE-90 TE-90 TE-90 TE-90 Surlyn ® Cover 9020 Composi-tion Properties of Molded Finished Balls: Compression 63 63 69 70 61C.O.R. .784 .778 .780 .770 .757 Shore C 88 88 88 88 89 Hardness Spin8,825 8,854 8,814 8,990 8,846 (R.P.M.) Cut 3-4 3-4 3-4 3-4 1-2Resistance

As it will be noted in finished balls 1-4, by creating a multi-layercover utilizing the high acid ionomer resins in the inner cover layerand the hard/soft low acid ionomer resin in the outer cover layer,higher compression and increased spin rates are noted over the singlelayer covers of Table 5. In addition, both the C.O.R. and the Shore Chardness are reduced over the respective single layer covers of Table 5.This was once again particularly true with respect to the multi-layeredballs containing the high acid ionomer resin in the inner layer (i.e.finished balls 1-4). In addition, with the exception of prior art ball 5(i.e. the '193 patent), resistance to cutting remains good but isslightly decreased. As noted above, the prior art ball of the '193patent suffers substantially in durability (as well as in resiliency) incomparison to the balls of the invention.

Furthermore, it is also noted that the use of the high acid ionomerresins as the inner cover material produces a substantial increase inthe finished balls' overall distance properties. In this regard, thehigh acid ionomer resin inner covers of balls 1-3 produce an increase ofapproximately 10 points in C.O.R. over the low acid ionomer resin innercovers of balls 4 and about a 25 point increase over the prior art balls5. Since an increase in 3 to 6 points in C.O.R. results in an averageincrease of about 1 yard in distance, such an improvement is deemed tobe significant.

Several other outer layer formulations were prepared and tested bymolding them around the core and inner cover layer combination to formballs each having a diameter of about 1.68 inches. First, B.F.GoodrichEstane® X4517 polyester polyurethane was molded about the core moldedwith inner layer cover formulation A. DuPont Surlyn® 9020 was moldedabout the core which was already molded with inner layer D. Similarproperties tests were conducted on these golf balls and the results areset forth in Table 6B below:

TABLE 6B Finish Balls Ingredients: 6 7 Inner Cover Layer A D CompositionOuter Cover Layer Estane ® 4517 Surlyn ® 9020 Composition Properties ofMolded Finished Balls: Compression 67 61 C.O.R. .774 .757 Shore CHardness 74 89 Spin (R.P.M.) 10,061 8,846 Cut Resistance 3-4 1-2

The ball comprising inner layer formulation D and Surlyn® 9020identifies the ball in the Nesbitt U.S. Pat. No. 4,431,193 patent. As isnoted, the example provides for relatively high softness and spin ratethough it suffers from poor cut resistance and low C.O.R. This ball isunacceptable by today's standards.

As for the Estane® X4517 polyester polyurethane, a significant increasein spin rate over the TE-90 cover is noted along with an increasedcompression. However, the C.O.R. and Shore C values are reduced, whilethe cut resistance remains the same. Furthermore, both the Estane® X4517polyester polyurethane and the Surlyn® 9020 were relatively difficult tomold in such thin sections.

EXAMPLE 2

In order to analyze the change in characteristics produced bymulti-layer golf balls (standard size) having inner cover layerscomprised of ionomer resin blends of different acid levels, a series ofexperiments were run. Specifically, 14 tests were performed, varying thetype of core, inner cover layer and outer cover layer. The results areshown below:

TABLE 7 Sample INNER COMP/ OUTER COMP SHORE # Core LAYER THICKNESS CORCOVER THICKNESS (Rhiele) COR D SPIN 8 1042 YELLOW NONE — SEE BELOW TOPGRADE 0.055 61 .800 68 7331 9 1042 YELLOW NONE — SEE BELOW 959/9600.055″ 56 .808 73 6516 10 SPECIAL 1.4″ 959/960 0/050″ 65/.805 959/9600.055″ 48 .830 73 6258 11 1042 YELLOW NONE — SEE BELOW SD 90 0.055″ 62.792 63 8421 12 SPECIAL 1.4″ TOP GRADE 0.050″ 66/.799 SD 90 0.055″ 55.811 63 8265 13 SPECIAL 1.4″ 959/960 0.050″ 65/.895 SD 90 0.055″ 53 .81363 8254 14 SPECIAL 1.4″ TOP GRADE 0.050″ 66/.799 TOP GRADE 0.055″ 51.819 68 7390 15 1042 YELLOW NONE — SEE BELOW Z-BALATA 0.055″ 67 .782 559479 16 SPECIAL 1.4″ 959/960 0.050″ 65/.805 Z-BALATA 0.055″ 61 .800 559026 17 SPECIAL 1.4″ TOP GRADE 0.050″ 66/.799 Z-BALATA 0.055″ 60 .798 559262 1042 YELLOW > COMP = 72, COR = .780 SPECIAL 147″ CORE > COMP = 67,COR = .782

In this regard, Top Grade or TG is a low acid inner cover ionomer resinblend comprising of 70.6% lotek® 8000, 19.9% lotek® 7010 and 9.6% whitemasterbatch. “959/960” is a 50/50 wt/wt blend of lotek® 959/960. In thisregard, Escor® or lotek® 959 is a sodium ion neutralizedethylene-acrylic neutralized ethylene-acrylic acid copolymer. Accordingto Exxon, lotek® 959 and 960 contain from about 19.0 to about 21.0% byweight acrylic acid with approximately 30 to about 70 percent of theacid groups neutralized with sodium and zinc ions, respectively. Thephysical properties of these high acid acrylic acid based ionomers areas follows:

ESCOR ® ESCOR ® PROPERTY (IOTEK ®) 959 (IOTEK ®) 960 Melt Index, g/10min 2.0 1.8 Cation Sodium Zinc Melting Point, ° F. 172 174 VicatSoftening Point, ° F. 130 131 Tensile @ Break, psi 4600 3500 Elongation@ Break, % 325 430 Hardness, Shore D 66 57 Flexural Modulus, psi 66,00027,000

Furthermore, the low acid ionomer formulation for SD 90 and Z-Balata areset forth below:

SD Cover ZB Cover 17.2% Surlyn ® 8320   19% Iotek ® 8000  7.5% Surlyn ®8120   19% Iotek ® 7030   49% Surlyn ® 9910 52.5% Iotek ® 7520 16.4%Surlyn ® 8940  9.5% white MB  9.7% white MB

The data clearly indicates that higher C.O.R. and hence increase traveldistance can be obtained by using multi-layered covered balls versusballs covered with single layers. However, some sacrifices incompression and spin are also noted. Further, as shown in comparingExample Nos. 12 vs. 13, Example Nos. 17 vs. 16, etc., use of lower acidlevel inner cover layers and relatively soft outer cover layers (i.e.,50 wt. % or more soft ionomer) produces softer compression and higherspin rates than the golf balls comprised of high acid inner coverlayers. Consequently, use of blends of low acid ionomer resins toproduce the inner layer of a multi-layer covered golf ball produces notonly enhanced travel distance but also enhanced compression and spinproperties.

EXAMPLE 3

Multi-layer oversized golf balls were produced utilizing differentionomer resin blends as the inner cover layer (i.e., core plus innercover layer is defined as “mantel”). The “ball data” of the oversizedmulti-layer golf balls in comparison with production samples ofTop-Flite® XL and Top-Flite® Z-Balata is set forth below.

TABLE 8 21 22 Top-Flite ® Top-Flite ® 18 19 20 XL Z-Balata 90 Core DataSize 1.43 1.43 1.43 1.545 1.545 COR .787 .787 .787 — — Mantle DataMaterial TG TG TG — — Size 1.61 1.61 1.61 — — Thickness .090 .090 .090 —— Shore D 68 68 68 — Compression 57 57 57 — — COR .815 .815 .815 — —Ball Data Cover TG ZB SD TG ZB Size 1.725 1.723 1.726 1.681 1.683 Weight45.2 45.1 45.2 45.3 45.5 Shore D 68 56 63 68 56 Compression 45 55 49 5377 COR .820 .800 .810 .809 .797 Spin 7230 9268 8397 7133 9287

The results indicate that use of multi-layer covers enhances C.O.R. andtravel distance. Further, the data shows that use of a blend of low acidionomer resins (i.e., Top Grade) to form the inner cover layer incombination with a soft outer cover (ZB or SD) produces enhanced spinand compression characteristics. The overall combination results in arelatively optimal golf ball with respect to characteristics of traveldistances, spin and durability.

EXAMPLE 4 Castable Polyurethane Covered Multi-layer Balls

A limited number of samples were made using BASF Baytec® RE232polyurethane as a cover material over four different types of mantlecores. Controls included Z-Balata 100s along with the same mantle coresused for the polyurethane samples covered with Z-Balata cover stock.Mantle cores were made up of 82 and 58 compression cores covered withlotek® 8030/7030.

Castable PU Molding Process

Materials used:

Baytec® RE832, mix ratio 9 parts A/12 parts B

1—1.57″ i.d. smooth cavity

2—1.68″ i.d. dimpled cavities

1—2″ hose clamp

1—bench vise or large C-clamp

The mantle core is 1.57″ and fits snugly in the 1.57″ cavity. The hoseclamp is attached to the 1.57′ cavity and a mantle core is placed ininside. Urethane is mixed and poured into one of the dimpled cavitiesand the two halves are placed together and clamped, forcing out excessmaterial and forming half the cover. The hose clamp is used to keep thetwo mold halves aligned during curing. When the cover material is set upenough (about 5 minutes), the two halves are separated and the 1.57″mold is replaced with the other 1.68″ mold and the process is repeated.Both halves of the cover are now cast and the entire assemble is placedin an 125° F. oven for 1 hour after which it can be opened and the ballremoved.

All samples were finished using normal production equipment andprocedures. The properties of the finished balls are set forth below:

TABLE 9 23 23 24 25 26 27 28 29 Core Data Size 1.47″ 1.47″ 1.47″ 1.47″1.47 1.47″ 1.47″ 1.47″ Weight 32.2 32 32.2 32 31.7 32.2 32 32.2 Comp 8258 82 58 85 82 58 82 COR 768 772 768 772 794 768 772 768 Mantle DataIotek ® Iotek ® Iotek ® Iotek ® Iotek ® Iotek ® Iotek ® Material8030/7030 8030/7030 8030/7030 8030/7030 None 8030/7030 8030/70308030/7030 Weight 37.8 38.1 37.9 38.1 37.8 38.1 37.9 Size 1.57″ 1.57″1.57″ 1.57″ 1.57″ 1.57″ 1.57″ Comp 70 48 69 48 70 48 69 COR 781 785 786788 781 785 786 Ball Data Cover Material Baytec ® RE832 Baytec ® RE832Baytec ® RE832 Baytec ® RE832 Z-Balata Z-Balata Z-Balata Z-Balata Weight45.4 45.5 45.5 45.2 45.3 44.8 45 Comp 75 64 73 60 80 66 Sn 65 COR 771763 770 761 792 775 774 778 Shore C 65 65 65 65 84 84 84 84 Spin (rpm)9560 8789 9285 8780 8796 8702 9072 8643 Cut 2 2 2 1.5 2 2 2 2 (1-good,4-poor) Scuff 1.5 1.5 1.5 1.5 2 3 3 3 (1-good, 4-poor)

Table 9 contains the construction details and test results. Multilayerballs with the thermoset urethane covers (Examples 23-25) were softer incompression and similar in COR to the multi-layer balls with theZ-Balata cover (Examples 27-29). Shore C was much lower for the urethaneballs and they were more resistant to scuff than any of the Z-Balatacovered balls. Guillotine cut resistance was about the same. Spin ratecomparison shows that the urethane samples are better than the Z-Balatacovered balls.

Test results indicate that a very good multi-layer ball can be madeusing castable polyurethane cover material. Further, advantages includethe molding of very thin covers, molding over very soft compressioncore/mantle, and low cost tooling.

The invention has been described with reference to the preferredembodiment. Obviously, modifications and alterations will occur toothers upon reading and understanding the preceding detaileddescription. It is intended that the invention, be construed asincluding all such modifications and alterations insofar as they comewithin the scope of the appended claims or the equivalents thereof.

I claim:
 1. A golf ball comprising: a core; an inner cover layerdisposed on said core, said inner cover layer having a Shore D hardnessof at least 60, said inner cover layer comprising a blend of two or morelow acid ionomer resins, each containing no more than 16% by weight ofan alpha, beta-unsaturated carboxylic acid; and an outer cover layerdisposed on said inner cover layer, said outer cover layer having aShore D hardness of about 64 or less, a thickness of from about 0.01 toabout 0.07 inches, and comprising a polyurethane material.
 2. The golfball of claim 1 wherein said outer cover layer has a thickness of fromabout 0.01 to about 0.05 inches.
 3. The golf ball of claim 1 whereinsaid outer cover layer has a thickness of from about 0.03 to about 0.06inches.
 4. A golf ball comprising: a core: an inner cover layer disposedabout said core, said inner cover layer having a Shore D hardness of atleast 60, said inner cover layer comprising a blend of two or moreionomeric resins, each containing no more than 16% by weight of analpha, beta-unsaturated carboxylic acid; and an outer cover layerdisposed on said inner cover layer, said outer cover layer having athickness of from about 0.01 to about 0.07 inches, and comprising apolyurethane material.
 5. The golf ball of claim 4 wherein said outercover exhibits a Shore D hardness of about 64 or less.
 6. The golf ballof claim 4 wherein said outer cover layer has a thickness of from about0.01 to about 0.05 inches.
 7. The golf ball of claim 4 wherein saidouter cover layer has a thickness of from about 0.03 to about 0.06inches.
 8. A golf ball comprising: a core: an inner cover layer disposedon said core, said inner cover layer having a Shore D hardness of about60 or more, said inner cover layer comprising an ionomeric resinincluding no more than 16% by weight of an alpha, beta-unsaturatedcarboxylic acid and having a modulus of from about 15,000 to about70,000 psi; and an outer cover layer disposed about said inner coverlayer, said outer cover layer having a thickness of from about 0.01 toabout 0.07 inches, and comprising a polyurethane material.
 9. The golfball of claim 8 wherein said outer cover exhibits a Shore D hardness ofabout 64 or less.
 10. The golf ball of claim 8 wherein said outer coverlayer has a thickness of from about 0.01 to about 0.05 inches.
 11. Thegolf ball of claim 8 wherein said outer cover layer has a thickness offrom about 0.03 to about 0.06 inches.